The very foundation of every male/female relationship is based on the man providing for the woman and making her feel secure. It once consisted of us bringing mammoth steaks back to the cave, but now it means providing a measure of financial security.
Asking her to lend you money completely shatters her faith in you to provide this basic function. She will question your money sense, your fiscal responsibility, heck, even your manhood. Ask a buddy, take out a loan, get another job do anything but hit your girl up for cash.